Aerial refueling systems aboard tanker aircraft are used to transfer fuel to receiver aircraft during flight. One type of aerial refueling system includes a hose and drogue. To perform refueling with this type of system, the tanker aircraft slows down from cruise speed to a lower refueling speed, and extends the hose and drogue. The drogue stabilizes the hose in flight and provides a funnel to aid insertion of the receiver aircraft's probe into a hose fuel coupling.
The hose and drogue are typically stored in a pod that is attached by a pylon to a lower outboard section of the tanker aircraft's wing. When deployed, the hose and drogue trail the pod.
During flight, airflow creates vortices trailing the pod. Vortex flow is circular in a vertical plane and has an upward velocity component which can lift the hose and drogue, thereby causing instability for the hose and drogue during extension and retraction. For older tanker aircraft, existing aerodynamic mitigation designs (e.g., chines and Gurney flaps) can counter low strength vortices across narrow regions of the refueling envelope.
A new class of tanker aircraft is being designed to operate at higher maximum speeds. The pod and its pylon may be designed to minimize buffet at maximum operating speed, but minimizing the buffet will cause higher side loads, which result in stronger vortices at refueling speeds. The existing mitigation designs are not effective for addressing significantly higher vortex strengths across the entire flight envelope.